The present invention relates to laser welding apparatus and method.
In recent years, laser welding is increasingly applied to robot welding. A Japanese Patent No. 3229834 shows such a laser welding technique of holding stationary a laser welding device attached to the tip of a robotic arm, and rotating a reflector inside the laser welding device to distribute a laser beam to each of a plurality of welding spots.
There is shown a laser welding technique of adjusting the focal length of a laser beam in accordance with different distances from a laser welding device to a is plurality of welding spots, in the datasheet of “FIBER ELEPHANT,” Number 0002243-01, published by ARGES GmbH, June 2003. If the focal length is adjusted by this laser welding technique, the spot size of the laser beam at focus changes with a change in the focal length. As a result, the amount or density of focused optical energy varies in accordance with the focal length. Accordingly, it may be necessary to adjust the time period of laser irradiation for each welding spot separately.
A Published Japanese Patent Application No. 2004-050246 shows a laser welding technique of holding the laser spot size at welding spot substantially constant between welding spots in order to cancel the differences in the laser focal spot size caused by a change in the laser focal length. This laser welding technique changes the laser focal length independently of the distance to each welding spot in such a manner that the laser spot size at welding spot is constant between welding spots, using a point apart from focus.